What does "Undefined function 'Handle' for input arguments of type 'Stateflow.Chart'." mean?

I keep getting the above error Generating Code after adding a matlab function to a stateflow chart. The Matlab function in this case uses coder.ceval to call some C code, but there are already similar matlab functions that do not have any issues. The matlab function is:

function [Valid, Length, StartAddr] = GetBlockInfo(Image, Index)
    % Initialise variables to set sizes
    Length = uint32(0);
    StartAddr = uint32(0);
    Valid = false;
    
    % Call the C code that gets the Block information
    Valid = coder.ceval('ImagesGetBlockInfo', Image, Index, coder.wref(StartAddr), coder.wref(Length));
end

The state flow chart is

Note commenting out the coder.ceval block does not enable the code generation.

This is the only change I have made to a model that previously generated successfully.

Also the Model can ge generated without any errors or warnings